The general type of insert involved here is illustrated in the United States patent to Hill, Nos. 3,097,417, which issued July 16, 1963. More recent patents include U.S. patents to Jones, 3,399,442, and to Seidel, 4,056,872, which show continuous grooves around the insert, and a U.S. patent to Contrucci, 3,487,515, which shows a flat radial extension of the central island of the insert to increase stability of the insert.
With the advent of the processing die method of shaping inserts, it becomes possible to incorporate configurations which could not be conveniently ground into an insert.
The present invention is directed to an insert design which is an improvement over previous designs and which lends itself to manufacture by the die-pressing methods currently used today for producing hard, wear and abrasion-resistant materials such as cemented hard metal carbides.
In state-of-the-art descending curves, cutting edge inserts with a continuous chip control groove, particularly with inserts having high rake angles, the thickness of the insert is substantially reduced and thinned along the center of the insert cutting edges, thereby weakening the insert at the center point. Another problem with continuous groove inserts lies in the press forming. Because the edge of the insert is narrowed centrally, there is a tendency for the insert to bulge out at the side edges after pressing and sintering. This results in an insert which is not a true square, triangle, or other polygon. With the present invention, the groove shape and center ridge to be described substantially reduces the need to compensate or correct for the center edge squeeze-out and thus provides a more accurate finished product.
The insert design of this invention utilizes straight line, V-shaped grooves extending inwardly and downwardly from and for a distance along the cutting edges and from each cutting corner. This groove distance totals about one-third of the side length of the insert for triangular, square, and large angle parallelogram insert styles; and is about one-half of the insert side length for small angle parallelogram insert styles. The outer faces of the grooves provide a positive rake angle when the insert is mounted in a negative rake holder. Then the grooves have a short level-off section, with a constant cross section. Near the center of the insert side length, the groove rises abruptly from the short level-off section to a crest or plateau of a reinforcing cross-ridge or midrise extending radially from the top and bottom faces or island.
This construction provides inserts of improved strength.
In state-of-the-art inserts employing curved line grooves, the rake angles vary continuously with distance from the cutting corner because of the groove curvature.
By contrast, inserts of this invention achieve constant rake angles over a broad range of depths of cuts because of the straight line groove design. The inserts provide good chip control, especially on light to medium depth cuts of up to about one-third of the cutting edge.
Furthermore, the rake angles can be selected to cover a broad range of the order of 5.degree. to 20.degree. positive rake, or greater if desired, when the inserts are placed in a negative rake holder.
Thus, the improved design is intended to have a wider range of machining capabilities.
Also, it is intended to provide both a greater area of support in a holding device and a stronger insert, thereby minimizing tool breakage.
Other objects and features of the invention will be apparent in the following description and claims in which the invention is set forth in a manner to enable those skilled in the art to practice the invention all in connection with the best modes presently contemplated by the inventors.